This invention relates to a photo-coupled semiconductor device commonly called a photo-coupler, and more particularly to improvements in the optical structure of such a device.
A photo-coupler has generally such a construction that a light-emitting element connected to an input terminal is disposed opposite to a light-receiving element or photosensitive element connected to an output terminal. In the photo-coupler, an electrical signal applied to the input terminal is converted once into light by the light-emitting element to be transmitted to the light-receiving element where the light is converted into the original electrical signal again to appear at the output terminal. Therefore, the photo-coupler is advantageous in that the input and output can be electrically isolated from each other. The photo-coupler having such an advantage is widely used as a signal transmission means between two coupled circuits in which there is a necessity for preventing electrical interference therebetween.
It is quite natural that one of the most important requirements for such a photo-coupler is a satisfactory efficiency of photo-coupling, and in order to provide a highest possible efficiency of photo-coupling, it is essential to improve the optical structure of the photo-coupling means between the light-emitting element and the light-receiving element.
While some proposals made heretofore in an effort to improve the optical structure of the photo-coupling means between the light-emitting element and the light-receiving element have been successful in improving the efficiency of photo-coupling to a certain extent, the prior art proposals have resulted in complexity of the structure of the photo-coupling means, and an undesirable reduction in the mass-productivity has been inevitably given rise to.
The light-emitting element used as the light source of the photo-coupler is classified into two types, that is, the type in which the light radiating surface lies in parallel to the light-emitting PN junction and the type in which the light radiating surface is disposed in orthogonal relation to the light-emitting PN junction. For conveniences of explanation, the former and latter types will be referred to hereinafter as a light-emitting element of vertically radiating type and a light-emitting element of horizontally radiating type, respectively. The light-emitting element of horizontally radiating type has a peculiar luminance distribution in its light radiating surface, and therefore, a photo-coupler having a very high efficiency of photo-coupling can be realized when the light-emitting element of this type is disposed opposite to the light-receiving element in such a relation that the luminance distribution of the light radiating surface of the former conforms to the photo-sensitivity distribution of the latter. In spite of the above fact, the light-emitting element of vertically radiating type has been mostly employed hitherto. One of the reasons therefore resides in the fact that the light-emitting element of horizontally radiating type requires a complex mounting structure which is not suitable for mass production.